Electrical machines are being used more and more frequently as drive units in drivetrains of motor vehicles (electric vehicles, hybrid vehicles). A basic property of the drivetrain of a motor vehicle is its ability to oscillate. This means that especially in a context of dynamic load changes, the rotation speed of the electrical machine can oscillate considerably despite an ideally smooth profile for the propulsion torque of the electrical machine. FIG. 1 shows, by way of example, a profile over time of a torque TELM of an electrical machine, and below it the rotation speed nELM of the electrical machine resulting therefrom. The oscillations that occur after the load change at t=1 s are clearly evident here. Such oscillations occur independently of the specific configuration of the drivetrain, and are observable both with “conventional” drivetrains and with drivetrains in which an electrical machine is coupled to a differential gearbox of a driven axle (“electric axle”) or directly to a wheel hub (“wheel hub drive system”). The oscillations that are introduced result, however, not only in impaired comfort but in an avoidable mechanical stress on the drivetrain.
DE 10 2005 015 484 A1 discloses a method for controlling a drivetrain of a vehicle having an internal combustion engine, at least one electrical machine, a fully automatic transmission, and at least one control device for controlling the internal combustion engine and the at least one electrical machine, in which method a load-change shock is avoided by pilot-controlling the at least one electrical machine.
DE 10 2004 039 756 A1 discloses a method for operating a drive system that encompasses an input drive device, an output drive device, and a connecting device connecting the output drive device with the input drive device. In this, a current oscillation state of the drive system is determined, and on the basis of this oscillation state at least one correction variable is generated and is applied at least indirectly to the drive system for oscillation damping. In order to determine the current oscillation state of the drive system, corresponding state variables at least of the input drive device, output drive device, and connecting device are ascertained.